The present invention is particularly adapted for use in connection with making hard patterns, as for example, cast iron patterns of the type commonly used in mass production of, for example, automotive parts. The present method for making such cast iron patterns is costly. Further, repair of cast iron patterns, which is frequently necessary after extensive use, is also very costly.
In the standard method for making a cast iron pattern, a master wood pattern is first made. This master pattern is what is termed a "double shrink" pattern. In casting, the pattern must be so dimensioned as to permit shrinkage to the metal which is cast. In making the conventional cast iron pattern, there is an intermediate step wherein a metallic wood or plastic pattern is made. A second dimensional configuration must be provided in the original master pattern to allow for such additional shrinkage. Additionally, a surplus of metal must be left in order to permit machining operations on the final pattern to finish it for production use.
The master pattern is sometimes used as a pattern in the casting process for making a cast iron or aluminum pattern. A metal pattern is machined to duplicate the original pattern minus one of the shrinks and the material machined off to finish the duplicating model. The duplicating model has sufficient material for one final shrink in the final pattern and for finishing the final pattern by machine operations. A female plastic or metal spotting fixture and male plastic or metal duplicating models are also made in the conventional method.
In the conventional method of making a cast iron pattern, the cast iron pattern that is cast from the wood master pattern is machined from a duplicating model that has only the final single shrink and this duplicating model may be constructed of wood, plastic, or metal. Today plastic is frequently used for duplicating models. More often a separate wood pattern is made to a single shrink and is used to make the plastic duplicating tooling. It may be used also to get an aluminum casting which is used after machining and bench work for duplicating purposes.
The final rough cast iron pattern must be machined, first by means of rough machining in which one of the duplicating models is conventionally used in automated machining processes. The final pattern is finished by bench work, by skilled tradesmen where it is ground, filed and scraped to result in the final, very accurate pattern. As will be appreciated, all of these steps, particularly the final machine and bench steps, are quite expensive.
Additionally, in use, such cast iron patterns do wear considerably as a result of abrasive action of the sand which is used to form molds. It is quite expensive to repair such patterns.
The present invention provides an inexpensive method for manufacturing a pattern which is useful in the same context as conventional patterns. Additionally, the pattern of the present invention is preferably fabricated of a material, such as nickel, which is highly resistant to the abrasive action of sand, thereby providing a long life for the pattern. The use of this method in the manufacture of core boxes should result in the design of much lighter, safer and less expensive core boxes and core machines.